University of Plymouth - Stages 1, 2 and 3 / Mbed OS Task532Solution

Task 5.2.3 Solution

main.cpp@2:212bbdc6a892, 2019-09-20 (annotated)

Committer:
noutram
Date:
Fri Sep 20 14:04:09 2019 +0000
Revision:
2:212bbdc6a892
Parent:
0:c616f46e44a5 
2019;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
noutram 0:c616f46e44a5 1 #include "mbed.h"
noutram 0:c616f46e44a5 2
noutram 0:c616f46e44a5 3 #define Fs 1000
noutram 0:c616f46e44a5 4 #define T (1.0/Fs)
noutram 0:c616f46e44a5 5 #define PI 3.1415926541
noutram 0:c616f46e44a5 6
noutram 0:c616f46e44a5 7
noutram 0:c616f46e44a5 8 //This GPIO is used for Chip Select
noutram 0:c616f46e44a5 9 DigitalOut DAC_CS(D10);
noutram 0:c616f46e44a5 10
noutram 2:212bbdc6a892 11 //SPI Object (temporarily remove JP6 when running this)
noutram 0:c616f46e44a5 12 SPI spi(D11, D12, D13);
noutram 0:c616f46e44a5 13
noutram 0:c616f46e44a5 14 //Ticker for setting the output sampling rate
noutram 0:c616f46e44a5 15 Ticker t;
noutram 0:c616f46e44a5 16
noutram 0:c616f46e44a5 17 //Discrete time
noutram 0:c616f46e44a5 18 unsigned int n=0;
noutram 0:c616f46e44a5 19
noutram 0:c616f46e44a5 20 //Frequency f
noutram 0:c616f46e44a5 21 double f = 10.0;
noutram 0:c616f46e44a5 22
noutram 0:c616f46e44a5 23 //Prototype for the ticker ISR
noutram 0:c616f46e44a5 24 void writeSample();
noutram 0:c616f46e44a5 25
noutram 0:c616f46e44a5 26 int main() {
noutram 0:c616f46e44a5 27
noutram 0:c616f46e44a5 28 //Set speed of the SPI interface
noutram 0:c616f46e44a5 29 spi.frequency(20000);
noutram 0:c616f46e44a5 30
noutram 0:c616f46e44a5 31 //16 bit words, mode 0 clock
noutram 0:c616f46e44a5 32 spi.format(16,0);
noutram 0:c616f46e44a5 33
noutram 0:c616f46e44a5 34 //Write at Fs Hz
noutram 0:c616f46e44a5 35 t.attach(writeSample, T);
noutram 0:c616f46e44a5 36
noutram 0:c616f46e44a5 37 while(1) {
noutram 0:c616f46e44a5 38 sleep();
noutram 0:c616f46e44a5 39 }
noutram 0:c616f46e44a5 40 }
noutram 0:c616f46e44a5 41
noutram 0:c616f46e44a5 42 //ISR for ticker
noutram 0:c616f46e44a5 43 void writeSample()
noutram 0:c616f46e44a5 44 {
noutram 0:c616f46e44a5 45 //Enable the selected slave device
noutram 0:c616f46e44a5 46 DAC_CS = 0;
noutram 0:c616f46e44a5 47
noutram 0:c616f46e44a5 48 //Write a header (top 4 bits) and value (bottom 12 bits)
noutram 0:c616f46e44a5 49 double y = cos(2.0*PI*n*f*T);
noutram 0:c616f46e44a5 50 unsigned int val = (unsigned int)(2048.0 * (y + 1.0));
noutram 0:c616f46e44a5 51 spi.write(0x7000 | val);
noutram 0:c616f46e44a5 52
noutram 0:c616f46e44a5 53 //Disable the selected slave device (and update the output)
noutram 0:c616f46e44a5 54 DAC_CS = 1;
noutram 0:c616f46e44a5 55
noutram 0:c616f46e44a5 56 n++;
noutram 0:c616f46e44a5 57 }